The present invention relates to improvements in tank constructions, particularly in upstanding open-top cable-wrapped fiberglass reinforced plastic tanks of the type disclosed in U.S. Pat. No. 3,025,992 which are especially suited to contain or store corrosive liquids.
This form of tank construction includes a cylindrical wall structure which may be formed and transported sectionally and thereafter assembled in situ. A steel cable is helically wrapped around the tank such that the vertical spacing between adjacent cable convolutions is closer near the bottom of the tank than at the top. Since this external cable operatively resists the hoop stress exerted on the tank wall by the liquid contained within the tank, the sectional wall structure may be manufactured to have an economically thin radial thickness.
However, as the wall structure is relatively thin in comparison to the tank diameter and height, the wall structure of the assembled tank is relatively flexible, particularly at its open upper end, and may deform or flex under normal wind loading when the tank is empty.
Moreover, such a tank, and other types of tank constructions, may have to be designed to resist seismic forces and wind forces which apply an overturning moment to the tank. Under application of such seismic forces, liquid within the tank may exert a hydrodynamic impulse on the wall structure, producing a tensile force in one portion thereof and a compressive force in another portion thereof.